Talk to us!
Hello, we are the scientific
team at Smart Fertilizer
How can we help you?
I have a question!
If you need agronomist consultation,
please visit our knowledge hub forum
Create a topic with your question
and team of our lead agronomists
will provide you with expert advice.

How can we call you?
Please sign up to explore our
articles and get your
lifetime access For Free
(Enter the same email if you have already registered Smart Fertilizer Knowledge Hub)
Plant Nutrition Experts Community
By subscribing to the newsletter you agree with Privacy Policy & Terms and Conditions

How to Balance Nutrient Solutions

Before we learn how to balance a nutrient solution, we must first understand what “A balanced nutrient solution” means.


Plants absorb mineral nutrients from aqueous solutions, whether it is a hydroponic nutrient solution or soil solution. Mineral nutrients are present in the nutrient solution as dissolved ions, which means they carry an electric charge.

Some mineral nutrients carry a positive charge (cations) and some carry a negative charge (anions).

There are specific ionic forms in which the plant can absorb nutrients. For example, Nitrogen can be absorbed either as NO3- or as NH4+.


Many refer to “balance” as the cation-anion balance. Is this the balance we are looking for in the nutrient solution?

In order to be able to calculate the cation-anion balance we need to be able to measure the number of charges. To do so, a unique unit must be used, a unit that integrates both the molecular weight of the ion and its charge.

This unit is the Equivalent.

The equivalent is calculated simply by multiplying the number of molecules of each ion (measured in moles) by the charge it carries.

For example, how many equivalents are in 80 grams of Calcium (Ca+2)?

The molecular weight of calcium is 40 grams/mole (1 mole = 6X1023 molecules).

Therefore, 80 grams of calcium are 2 moles.

Calcium carries a positive charge of +2.

Using the above definition of equivalent, we get 80 grams of Ca+2 = 2X2=4 equivalents.

In the same way, 248 grams of NO3- are also 4 equivalents. This means that 80 grams of calcium carry the same amount of charges as 248 NO3- does.

The cation-anion balance is calculated by comparing the number of equivalents of cations with the number of equivalents of anions.


To balance nutrient solutions and plan optimized fertilizer plans for your crops

Click here for the solution


Consider the following water analysis.

If we calculate the total anions and total cations in units of ppm, we get 311.69 ppm anions and 118.21 ppm cations.

N-NO3- 1.5  N-NH4+ 7.3
SO42- 81.48  K+ 9.62
Cl- 36  Ca+2 47.55
HCO3- 192.71  Mg+2 11.22
   Na+  42.52
 Total  311.69   Total  118.21

However, when we convert each anion and cation to meq/l and make the balance, the result is 5.99 meq/l anions and 5.94 meq/l cations (1 meq= 1/1000 of an equivalent).

N-NO3- 0.11 N-NH4+ 0.52
SO42- 1.7 K+ 0.25
Cl- 1.02 Ca+2 2.38
HCO3- 3.16 Mg+2 0.94
Na+ 1.85
Total 5.99 Total 5.94
Very close to a complete balance!

The difference is within the range of an acceptable measuring error.

Was this result achieved by chance?

Actually not…

According to the law of electroneutrality, the total charge of an aqueous solution must be zero.

∑ negatively charged ions = ∑ positively charged ions

This is a law of nature.

It brings us to conclusion # 1 – Water is ALWAYS balanced, with respect to cation-anion balance.


Easily create your fertilization plan with our software
Start Using and Increase Your Harvest up to 40%
Create your plan


To find an answer to this question, let’s first look at the composition of one fertilizer. We will use Calcium Nitrate as an example.

Composition in 100 grams in meq/l
N-NO3- 14.4% 14.4 1.03
N-NH4+ 1.1% 1.1 0.08
Ca+2 19% 19 0.95

We can see that the fertilizer is balanced with respect to cation-anion balance.

A surprise? Not exactly…

Being a salt, ANY fertilizer will always contain the same amounts of cations an anions, measured in equivalents (sum of electrical charges is zero).

So when we dissolve fertilizers to water, no matter which fertilizers and in which amounts, the resulted nutrient solution will always be balanced, with respect to cation-anion balance!

If so, why should we calculate this balance?

We do so in order to validate the water analysis / nutrient solution test results.

An error of more than 5% in the cation-anion balance might imply that the analysis is not accurate.

However, if the laboratory did not test for one of the major cations or anions, then a correct balance cannot be calculated.


All of the above conclusions are valid for the soil solution as well.

  • Recommends the ideal fertilizer mixture/ blends
  • Saves up to 50% on fertilizer costs
  • Comprehensive data on hundreds of crop varieties
  • Interprets test results for any extraction method

Try Our Software Now